Semiconductor fabrication techniques may be used to form shallow trench isolation (STI) or damascene inter layer dielectric (ILD) features, for example, using 248 nanometer (nm) or 193 nm wavelength lithography technology. To enable patterning of a feature into a substrate layer, the layer is masked with a sacrificial mask stack including a carbon-based hardmask layer, a silicon-based anti-reflective coating (ARC) layer and a photo resist layer. To form the masking stack, the carbon-based hardmask layer is deposited using a plasma enhanced chemical vapor deposition (PECVD) process to form an amorphous carbon material. Then, a silicon-based material, such as silicon nitride (Si3N4) or silicon-oxy-nitride (SiOxNy(Hz)), is deposited, for example using another PECVD or CVD process to form the silicon-based ARC layer. The thickness and stoichiometry of the silicon-based ARC layer is tuned to provide the ARC with the desired anti-reflective properties.
248 nm and 193 nm generation resist formulations used for the photo resist layer limit the ability of the photo resist layer to withstand an etch process required to define the feature in the substrate. Because it is therefore undesirable to use resist as a mask to etch the substrate, after the photo resist layer is defined with a pattern by a photolithography operation, each of the silicon-based ARC layer and the carbon-based hardmask layer are defined with a dry etch process. With the thickness of the photo resist layer limited by etch resistance and patterning resolution, the carbon-based hardmask layer is utilized as a sacrificial layer to transfer a pattern into the substrate using a third dry etch process.
The sacrificial mask stack, however, incurs significant overhead to the fabrication of devices. As noted, to define a single feature layer, multiple sacrificial non-photo definable masking materials must be deposited, defined then removed by etch processes. While a silicon-based ARC layer is needed to avoid interference problems during lithography, deposition of such a layer entails expensive silane-based gases. Furthermore, stripping of a sacrificial hardmask including a similar material as the feature layer may compromise the feature layer and lead to failure. For example, if the substrate is of a material similar to that of the silicon-based ARC layer, then it must be ensured that patterning of either the carbon-based hardmask layer or the substrate removes all of the silicon-based ARC layer, otherwise a strip process capable of removing residual silicon-based ARC layer would also damage the substrate.